<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        .active {
            color: red;
        }
    </style>
</head>
<body>
<div id="app">
    <!--    <h2 :class="active">{{message}}</h2>-->
    <h2 class="title" v-bind:class="{active: isActive, line: isLine}">{{message}}</h2>
    <h2 class="title" v-bind:class="getClasses()">{{message}}</h2>
    <button v-on:click="btnClick">button</button>
</div>

<script src="../js/vue.js"></script>
<script>
    const app = new Vue({
        el: '#app',
        data: {
            message: 'hi',
            isActive: true,
            isLine: true
        },
        methods: {
            btnClick: function () {
                this.isActive = !this.isActive
            },
            getClasses: function () {
                return {active: this.isActive, line: this.isLine}
            }
        }
    })
</script>
</body>
</html>